Plastic materials have the history that they have been developed in order to obtain highly durable materials which are hardly decomposed, and ironically, such high durability is now the cause of waste pollution, and in particular plastic pollution. To be more specific, conventional crosslinked cured products are not intended for chemical dissociation.
For example, a polysulfide polymer containing two or more thiol groups in the molecule is widely employed in sealants, coating compositions, adhesives and the like since such polysulfide polymer is capable of reacting with an epoxy, isocyanate, or the like which readily reacts with the thiol group to form a cured product with an increased molecular weight. A composition comprising a compound having hydroxyl group and a compound having two or more vinyl ether (enol ether) groups is also disclosed (EP 296507 A2), and this composition is claimed to be a curable composition which is free from substances that are toxic to human body such as an isocyanate or an aldehyde, which is safe since no toxic substance is discharged from the system, and which can be cured at a relatively low temperature into a product exhibiting excellent chemical and physical performance. These cured product, however, can not be softened or liquefied by chemical decomposition at the desired timing. With regard to the polysulfide polymer as mentioned above, cured product can be formed by using a metal oxide for the catalyst. However, the cured product is preferably free from such metal oxide in view of the safety and since inclusion of such metal oxide will necessitate further separation process.
Lately, there is a growing concern for protection of global environment including the problem of the waste pollution as mentioned above, and guidelines have been published to promote recycling by conducting the waste disposal in each industry or by item, for example, home appliance, OA equipment, and other commodities which enable efficient use of the resources. In correspondence with such situation, a strong demand exists for environmentally friendly materials which can be produced into recyclable products.
Biodegradable and photodegradable plastic materials have been developed in view of such situation. However, plastic materials should, on the other hand, perpetually retain its performance under normal conditions of use without undergoing degradation by decomposition or the like. Accordingly, there is an expectation for development of a thermally dissociatable material which thermally dissociates under temperature conditions which are different from the conditions of use and becomes liquefied or softened to enable disassembly of the structure to which this material has been adhered, and which, on the other hand, does not become degraded by decomposition while it is in use and retains its integrated (cured) conditions.
Conventional thermal dissociation technologies that have been known in the art include use of thermal dissociation in blocking technology of a curing system, and latent catalysts which become active by heat, light, moisture, oxygen, or other external stimulation, and blocking of functional group such as isocyanate group have been developed and put into practical use. For example, JP 4-175375 A discloses a one part thermosetting composition which is a composition comprising a hydroxyl group-containing compound and a vinyl ether group-containing compound further comprising a thermally latent acid catalyst.
JP 4-72324 A discloses a blocking technology of carboxyl group wherein carboxyl group in a thermosetting resin composition comprising a multifunctional vinyl (thio)ether compound having two or more vinyl (thio)ether groups and a compound having two or more carboxyl groups is blocked by monovinyl (thio)ether to form a hemi(thio)acetal ester group. However, the curing system utilizing such conventional blocking technology generally suffers from the problem after its curing that the component which is not involved in the reaction, for example, the blocking agent (protective group) either remains in the system or is discharged from the system in the thermal dissociation of the blocked compound, and such components results in the tack, toxicity, or contamination of the global environment.
Furthermore, the curing systems using the conventional blocking technology are silent about the thermal dissociation ability of the cured product obtained by such curing system.